Character Strings in C Programming

1
Character Strings Lesson
CS1313 Spring 2024
20.
The 
strlen
 Function
21.
 
strlen
 Function Example
22.
Dynamic Allocation of Strings
23.
String Dynamic Allocation Example
#1
24.
String Dynamic Allocation Example
#2
25.
Passing a String as a Function
Argument
26.
String Function Argument Example
#1
27.
String Function Argument Example
#2
28.
String Function Argument Example
#3
29.
String Comparisons
30.
String Comparison is Case Sensitive
31.
String Comparison Example #1
32.
String Comparison Example #2
33.
String Comparison Example #3
1.
Character Strings Lesson Outline
2.
 
char
 Arrays #1
3.
 
char
 Arrays #2
4.
Character Array Example #1
5.
Character Array Example #2
6.
Character Strings
7.
Character String Terminator
8.
Jargon: Sentinel Value
9.
Character String Assignment Example #1
10.
Character String Assignment Example #2
11.
 
#include <string.h>
12.
Character String Declaration
13.
Character String Terminator
14.
How String Printing Really Works #1
15.
How String Printing Really Works #2
16.
String Copy Function: 
strcpy
17.
 
strcpy
 Example
18.
String Placeholder
19.
String Placeholder Example
Character Strings Lesson Outline
2
Character Strings Lesson
CS1313 Spring 2024
In C, you can have an array of type
 
char
,
just as you can have arrays of numeric types:
char my_name[12];
We can fill this
 
char
 
array with characters and
be able to print them out.
char
 
Arrays #1
3
Character Strings Lesson
CS1313 Spring 2024
Is this a good solution?
my_name[ 0] = 'H';
my_name[ 1] = 'e';
my_name[ 2] = 'n';
my_name[ 3] = 'r';
my_name[ 4] = 'y';
my_name[ 5] = ' ';
my_name[ 6] = 'N';
my_name[ 7] = 'e';
my_name[ 8] = 'e';
my_name[ 9] = 'm';
my_name[10] = 'a';
my_name[11] = 'n';
char
 
Arrays #2
4
Character Strings Lesson
CS1313 Spring 2024
#include <stdio.h>
int main ()
{ /* main */
    const int my_name_length = 12;
    char my_name[my_name_length];
    int  index;
    my_name[ 0] = 'H';
    my_name[ 1] = 'e';
    my_name[ 2] = 'n';
    my_name[ 3] = 'r';
    my_name[ 4] = 'y';
    my_name[ 5] = ' ';
    my_name[ 6] = 'N';
    my_name[ 7] = 'e';
    my_name[ 8] = 'e';
    my_name[ 9] = 'm';
    my_name[10] = 'a';
    my_name[11] = 'n';
    printf("My name is ");
    for (index = 0; index < my_name_length; index++) {
        printf("%c", my_name[index]);
    } /* for index */
    printf(".\n");
    return 0;
} /* main */
Character Array Example #1
5
Character Strings Lesson
CS1313 Spring 2024
% 
gcc -o chararray chararray.c
% 
chararray
My name is Henry Neeman.
This is an improvement, but it’s still not an efficient way
to assign a sequence of characters to a variable.
What we want is a kind of
 
char
 
variable
that will be convenient to use for
inputting, outputting and using sequences of characters.
Character Array Example #2
6
Character Strings Lesson
CS1313 Spring 2024
A 
character string
 
is a sequence of characters with
the following properties:
it is 
stored
 
like a
 
char
 
array;
it is 
used
    
like a
 
char
 
scalar (kind of).
In C, we declare a character string like so:
char my_name[my_name_length+1];
Notice that a character string is
declared 
exactly
 
like a
 
char
 
array;
in fact, a character string 
is
 
a
 
char
 
array.
Character Strings
7
Character Strings Lesson
CS1313 Spring 2024
The only 
difference
 between a
 
char
 
array
 and
a character 
string
 is that the 
length
 of the
 
char
 
string
is 
one greater
 
than the number of characters to be stored,
and the last character in any C character string is
the 
null character
, called
 
NUL
, which corresponds to
integer value 0:
'\0'
A 
null character
 (integer 0) used to indicate the end of a string
is known as a 
character string terminator
.
In general, a numeric value that is used to indicate that a
particular state has been reached – for example, the end of
a list – is called a 
sentinel
 
value.
So, the character string terminator
 
NUL
 
is a sentinel
that indicates the end of the string in question.
Character String Terminator
Jargon: Sentinel Value
A 
sentinel value
 is a numeric value – a number – that means
something qualitative, even though it’s in a variable whose value is
intended to be a number.
For example, the individual characters in a character string are
actually ASCII numeric values that encode the individual
characters, as we saw in the ASCII table.
But the string terminator isn’t a character as such; it’s a value whose
purpose is to indicate that the end of the string has been reached.
Another example is in weather data. For example, in a 3D array of
of wind velocity (expressed in, e.g., km per hour), a value like
-99999 might mean “no wind velocity measured in this location,”
for example if that location were inside the rocky interior of a
mountain.
Character Strings Lesson
CS1313 Spring 2024
8
9
Character Strings Lesson
CS1313 Spring 2024
% 
cat charstrassnbad.c
#include <stdio.h>
int main ()
{ /* main */
    const int my_name_length       = 12;
    const int program_success_code =  0;
    char my_name[my_name_length + 1];
    my_name = "Henry Neeman"; /* 
<-- DOESN
'
T WORK! */
    printf("My name is %s.\n", my_name);
    return program_success_code;
} /* main */
% 
gcc -o charstrassnbad charstrassnbad.c
charstrassnbad.c: In function ‘main’:
charstrassnbad.c:8: incompatible types
  in assignment
The version above seems like it should work, but it doesn’t!
Character String Assignment Example #1
10
Character Strings Lesson
CS1313 Spring 2024
% 
cat charstrassn.c
#include <stdio.h>
#include <string.h>
int main ()
{ /* main */
    const int my_name_length       = 12;
    const int program_success_code =  0;
    char my_name[my_name_length + 1];
    
strcpy(my_name, "Henry Neeman"); /* <-- WORKS! */
strcpy(my_name, "Henry Neeman"); /* <-- WORKS! */
    printf("My name is %s.\n", my_name);
    return program_success_code;
} /* main */
% 
gcc -o charstrassn charstrassn.c
% 
charstrassn
My name is Henry Neeman.
This version works!
Character String Assignment Example #2
#include <string.h>
When using string functions in C such as 
strcpy
,
you 
MUST
 add the following preprocessor directive to
your C source file, just after the directive for 
stdio.h
, like so:
#include <stdio.h>
#include <string.h>
Character Strings Lesson
CS1313 Spring 2024
11
12
Character Strings Lesson
CS1313 Spring 2024
In C, we declare a 
character string
 like so:
char my_name[my_name_length+1];
Notice that a character string is declared
exactly like
 a
 
char
 
array; in fact, it 
is
 
a
 
char
 
array.
The only difference in the declaration is that the length of
the array of
 
char
 
elements that represents the string is
one greater
 than the length of the string.
Character String Declaration
13
Character Strings Lesson
CS1313 Spring 2024
The last character in any C character string is the
null character
, called
 
NUL
, which corresponds to
integer value 0:
'\0'
Thus, the 
null character
 (integer 0) is often referred to as the
character string terminator
.
In general, a numeric value that is used to indicate that a
particular state has been reached – for example, the end of a
list – is called a 
sentinel
 
value.
So, the character string terminator
 
NUL
 
is a sentinel that
indicates the end of the string in question.
Character String Terminator
14
Character Strings Lesson
CS1313 Spring 2024
% 
cat charstrassn.c
#include <stdio.h>
#include <string.h>
int main ()
{ /* main */
    const int my_name_length       = 12;
    const int program_success_code =  0;
    char my_name[my_name_length + 1];
    strcpy(my_name, "Henry Neeman");
    printf("My name is %s.\n", my_name);
    return program_success_code;
} /* main */
% 
gcc -o charstrassn charstrassn.c
% 
charstrassn
My name is Henry Neeman.
The program on the next page behaves 
identically
 to this
program.
How String Printing Really Works #1
15
Character Strings Lesson
CS1313 Spring 2024
% 
cat printstring.c
#include <stdio.h>
#include <string.h>
int main ()
{ /* main */
    const int my_name_length       = 12;
    const int program_success_code =  0;
    char my_name[my_name_length + 1];
    int  index;
    strcpy(my_name, "Henry Neeman");
    printf("My name is ");
    index = 0;
    while (my_name[index] != '\0') {
        printf("%c", my_name[index]);
        index++;
    } /* while (my_name[index] != '\0') */
    printf(".\n");
    return program_success_code;
} /* main */
% 
gcc -o printstring printstring.c
% 
printstring
My name is Henry Neeman.
How String Printing Really Works #2
16
Character Strings Lesson
CS1313 Spring 2024
The C standard library function
 
strcpy
 
copies a character string
into a
 
char
 
array.
strcpy(my_name, "Henry Neeman");
Notice that you
CANNOT SIMPLY ASSIGN ONE STRING TO ANOTHER
:
 /* THIS WON'T WORK! */
  my_name = "Henry Neeman"; /* NO! */
String Copy Function:
 
strcpy
17
Character Strings Lesson
CS1313 Spring 2024
% 
cat charstrcpy.c
#include <stdio.h>
#include <string.h>
int main ()
{ /* main */
    const int my_name_length       = 12;
    const int program_success_code =  0;
    char my_name[my_name_length + 1];
    char my_name2[my_name_length + 1];
    strcpy(my_name, "Henry Neeman");
    printf("My name is %s.\n", my_name);
    strcpy(my_name2, my_name);
    printf("My name is %s.\n", my_name2);
    return program_success_code;
} /* main */
% 
gcc -o charstrcpy charstrcpy.c
% 
charstrcpy
My name is Henry Neeman.
My name is Henry Neeman.
strcpy
 
Example
18
Character Strings Lesson
CS1313 Spring 2024
In a
 
printf
 
statement, the placeholder for a character
string is:
%s
String Placeholder
19
Character Strings Lesson
CS1313 Spring 2024
% 
cat charstrcpy.c
#include <stdio.h>
#include <string.h>
int main ()
{ /* main */
    const int my_name_length       = 12;
    const int program_success_code =  0;
    char my_name[my_name_length + 1];
    char my_name2[my_name_length + 1];
    strcpy(my_name, "Henry Neeman");
    printf("My name is 
%s
.\n", my_name);
    strcpy(my_name2, my_name);
    printf("My name is 
%s
.\n", my_name2);
    return program_success_code;
} /* main */
% 
gcc -o charstrcpy charstrcpy.c
% 
charstrcpy
My name is Henry Neeman.
My name is Henry Neeman.
String Placeholder Example
20
Character Strings Lesson
CS1313 Spring 2024
The C Standard Library function
 
strlen
 
returns the length
of the string that is passed to it, 
EXCLUDING THE
STRING TERMINATOR
:
my_name_length = strlen(my_name);
The
 
strlen
 
Function
21
Character Strings Lesson
CS1313 Spring 2024
% 
cat charstrlen.c
#include <stdio.h>
#include <string.h>
int main ()
{ /* main */
    printf("strlen(%cHenry Neeman%c) = %d\n",
        '\042', '\042', strlen("Henry Neeman"));
    return 0;
} /* main */
% 
gcc -o charstrlen charstrlen.c
% 
charstrlen
strlen("Henry Neeman") = 12
strlen
 
Function Example
22
Character Strings Lesson
CS1313 Spring 2024
You can dynamically allocate the space for a string, just as
you can for any other array:
my_name =
    (char*)malloc(sizeof(char) *
                  (my_name_length + 1));
Dynamic Allocation of Strings
23
Character Strings Lesson
CS1313 Spring 2024
% 
cat charstrdyn.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main ()
{ /* main */
    const int program_success_code =  0;
    const int program_failure_code = -1;
    char* my_name = (char*)NULL;
    int   my_name_length;
String Dynamic Allocation Example #1
24
Character Strings Lesson
CS1313 Spring 2024
    my_name_length = strlen("Henry Neeman");
    my_name =
        (char*)malloc(sizeof(char) *
                      (my_name_length + 1));
    if (my_name == (char*)NULL) {
        printf("ERROR: can’t allocate ");
        printf("char array my_name.\n");
        exit(program_failure_code);
    } /* if (my_name == (char*)NULL) */
    strcpy(my_name, "Henry Neeman");
    printf("My name is %s.\n", my_name);
    free(my_name);
    my_name = (char*)NULL;
    return program_success_code;
} /* main */
% 
gcc -o charstrdyn charstrdyn.c
% 
charstrdyn
My name is Henry Neeman.
String Dynamic Allocation Example #2
25
Character Strings Lesson
CS1313 Spring 2024
Passing a string to a function as an argument is
just like passing  any other kind of array argument,
whether statically allocated or dynamically allocated,
except that you  
DON’T
 also need to pass a length argument
(because its length is implied by its string terminator):
int main ()
{ /* main */
    char my_name[my_name_length + 1];
    char* my_name2 = (char*)NULL;
    ...
    print_a_string(my_name);
    ...
    print_a_string(my_name2);
    ...
} /* main */
void print_a_string (char* the_string)
Passing a String as a Function Argument
26
Character Strings Lesson
CS1313 Spring 2024
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main ()
{ /* main */
    const int my_name_length       = 12;
    const int program_success_code =  0;
    const int program_failure_code = -1;
    char my_name[my_name_length + 1];
    char* my_name2 = (char*)NULL;
    void print_a_string(char* the_string);
String Function Argument Example #1
27
Character Strings Lesson
CS1313 Spring 2024
    strcpy(my_name, "Henry Neeman");
    printf("My name is %s.\n", my_name);
    print_a_string(my_name);
    my_name2 =
        (char*)malloc(sizeof(char) *
                      (strlen(my_name) + 1));
    if (my_name2 == (char*)NULL) {
        printf("ERROR: can’t allocate ");
        printf("char array my_name2.\n");
        exit(program_failure_code);
    } /* if (my_name2 == (char*)NULL) */
    strcpy(my_name2, my_name);
    printf("My name is still %s.\n", my_name);
    print_a_string(my_name2);
    free(my_name2);
    my_name2 = (char*)NULL;
    return program_success_code;
} /* main */
String Function Argument Example #2
28
Character Strings Lesson
CS1313 Spring 2024
void print_a_string (char* the_string)
{ /* print_a_string */
    const int program_failure_code = -1;
    printf("The string that was passed is:\n");
    if (the_string == (char*)NULL) {
        printf("ERROR: can’t print a ");
        printf("non-existent string\n");
        printf(" in print_a_string.\n");
        exit(program_failure_code);
    } /* if (the_string == (char*)NULL) */
    printf("%s\n", the_string);
} /* print_a_string */
% 
gcc -o charstrpass charstrpass.c
% 
charstrpass
My name is Henry Neeman.
The string that was passed is:
Henry Neeman
My name is still Henry Neeman.
The string that was passed is:
Henry Neeman
String Function Argument Example #3
29
Character Strings Lesson
CS1313 Spring 2024
Just as numeric values can be compared, so can string values.
However, strings aren’t scalars.
In C, two strings are defined to be equal if they have
the exact same contents.
In C, strings are compared using the
 
strcmp
 
function from
the C Standard Library.
The relational operators CANNOT CANNOT CANNOT
be used to compare strings!
==  !=  <  <=  >  >=
String Comparisons
30
Character Strings Lesson
CS1313 Spring 2024
String comparison is 
case sensitive
.
Thus, if two strings are identical, except that, in a single
character, they differ by case – for example, an
 
"H"
 
for
one string corresponds to an
 
"h"
 
for the other –
then they 
WON’T
 be equal.
For example:
"Henry"
 
is not equal to
 
"henry"
String Comparison is Case Sensitive
31
Character Strings Lesson
CS1313 Spring 2024
#include <stdio.h>
#include <string.h>
int main ()
{ /* main */
    const int my_name_length       = 12;
    const int program_success_code =  0;
    char my_name[my_name_length + 1];
    char my_name2[my_name_length + 1];
    char my_first_name[my_name_length + 1];
    char my_first_name_lower[my_name_length + 1];
    char my_last_name[my_name_length + 1];
String Comparison Example #1
32
Character Strings Lesson
CS1313 Spring 2024
    strcpy(my_name, "Henry Neeman");
    strcpy(my_name2, my_name);
    strcpy(my_first_name, "Henry");
    strcpy(my_first_name_lower, "henry");
    strcpy(my_last_name, "Neeman");
    printf("strcmp(%s,%s) = %2d\n",
        my_name, my_name2,
        strcmp(my_name, my_name2));
    printf("strcmp(%s,%s) = %2d\n",
        my_first_name, my_first_name_lower,
        strcmp(my_first_name, my_first_name_lower));
    printf("strcmp(%s,%s) = %2d\n",
        my_last_name, my_first_name,
        strcmp(my_last_name, my_first_name));
    return program_success_code;
} /* main */
String Comparison Example #2
33
Character Strings Lesson
CS1313 Spring 2024
% 
gcc -o charstrcmp charstrcmp.c
% 
charstrcmp
strcmp(Henry Neeman,Henry Neeman) = 0
strcmp(Henry,henry) = -1
strcmp(Neeman,Henry) = 1
Notice that the return value for
 
strcmp
 
can be interpreted as:
zero
:        the strings are equal
negative
: the first string is less
positive
:  the first string is greater
String Comparison Example #3

								

								

								

										

												
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Dive into the world of character strings in C programming with topics like string declaration, termination, copying functions, comparisons, and dynamic allocation. Explore how to work with character arrays and pass strings as function arguments for effective programming. Enhance your knowledge through examples and lessons in managing character strings efficiently.


								
    
																		
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  •    Character strings
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  •    String manipulation
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Presentation Transcript

								

								
  1. Character Strings Lesson Outline 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Character String Assignment Example #2 11.  #include <string.h> 12. Character String Declaration 13. Character String Terminator 14. How String Printing Really Works #1 15. How String Printing Really Works #2 16. String Copy Function: strcpy 17.  strcpy Example 18. String Placeholder 19. String Placeholder Example Character Strings Lesson Outline char Arrays #1 char Arrays #2 Character Array Example #1 Character Array Example #2 Character Strings Character String Terminator Jargon: Sentinel Value Character String Assignment Example #1 20. The strlen Function 21.  strlen Function Example 22. Dynamic Allocation of Strings 23. String Dynamic Allocation Example  #1 24. String Dynamic Allocation Example  #2 25. Passing a String as a Function  Argument 26. String Function Argument Example  #1 27. String Function Argument Example  #2 28. String Function Argument Example  #3 29. String Comparisons 30. String Comparison is Case Sensitive 31. String Comparison Example #1 32. String Comparison Example #2 33. String Comparison Example #3 Character Strings Lesson CS1313 Spring 2024 1
    2. 
            
            
            
  2. char Arrays #1 In C, you can have an array of type char,                           just as you can have arrays of numeric types: char my_name[12]; We can fill this char array with characters and                   be able to print them out. Character Strings Lesson CS1313 Spring 2024 2
    3. 
            
            
            
  3. char Arrays #2 my_name[ 0] = 'H'; my_name[ 1] = 'e'; my_name[ 2] = 'n'; my_name[ 3] = 'r'; my_name[ 4] = 'y'; my_name[ 5] = ' '; my_name[ 6] = 'N'; my_name[ 7] = 'e'; my_name[ 8] = 'e'; my_name[ 9] = 'm'; my_name[10] = 'a'; my_name[11] = 'n'; Is this a good solution? Character Strings Lesson CS1313 Spring 2024 3
    4. 
            
            
            
  4. Character Array Example #1 #include <stdio.h> int main () { /* main */     const int my_name_length = 12;     char my_name[my_name_length];     int  index;     my_name[ 0] = 'H';     my_name[ 1] = 'e';     my_name[ 2] = 'n';     my_name[ 3] = 'r';     my_name[ 4] = 'y';     my_name[ 5] = ' ';     my_name[ 6] = 'N';     my_name[ 7] = 'e';     my_name[ 8] = 'e';     my_name[ 9] = 'm';     my_name[10] = 'a';     my_name[11] = 'n';     printf("My name is ");     for (index = 0; index < my_name_length; index++) {         printf("%c", my_name[index]);     } /* for index */     printf(".\n");     return 0; } /* main */ Character Strings Lesson CS1313 Spring 2024 4
    5. 
            
            
            
  5. Character Array Example #2 % gcc -o chararray chararray.c % chararray My name is Henry Neeman. This is an improvement, but it   s still not an efficient way        to assign a sequence of characters to a variable. What we want is a kind of char variable                              that will be convenient to use for                              inputting, outputting and using sequences of characters. Character Strings Lesson CS1313 Spring 2024 5
    6. 
            
            
            
  6. Character Strings A character stringis a sequence of characters with               the following properties:     it is stored like a char array;     it is used    like a char scalar (kind of). In C, we declare a character string like so: char my_name[my_name_length+1]; Notice that a character string is                                       declared exactly like a char array;                                   in fact, a character string is a char array. Character Strings Lesson CS1313 Spring 2024 6
    7. 
            
            
            
  7. Character String Terminator The only difference between a char array and                       a character string is that the length of the char string is one greater than the number of characters to be stored,      and the last character in any C character string is                  the null character, called NUL, which corresponds to         integer value 0: '\0' A null character (integer 0) used to indicate the end of a string  is known as a character string terminator. In general, a numeric value that is used to indicate that a  particular state has been reached     for example, the end of      a list     is called a sentinelvalue. So, the character string terminator NUL is a sentinel              that indicates the end of the string in question. Character Strings Lesson CS1313 Spring 2024 7
    8. 
            
            
            
  8. Jargon: Sentinel Value A sentinel value is a numeric value     a number     that means  something qualitative, even though it   s in a variable whose value is  intended to be a number. For example, the individual characters in a character string are  actually ASCII numeric values that encode the individual  characters, as we saw in the ASCII table. But the string terminator isn   t a character as such; it   s a value whose  purpose is to indicate that the end of the string has been reached. Another example is in weather data. For example, in a 3D array of  of wind velocity (expressed in, e.g., km per hour), a value like          -99999 might mean    no wind velocity measured in this location,     for example if that location were inside the rocky interior of a  mountain. Character Strings Lesson CS1313 Spring 2024 8
    9. 
            
            
            
  9. Character String Assignment Example #1 % cat charstrassnbad.c #include <stdio.h> int main () { /* main */     const int my_name_length       = 12;     const int program_success_code =  0;     char my_name[my_name_length + 1];     my_name = "Henry Neeman"; /* <-- DOESN'T WORK! */     printf("My name is %s.\n", my_name);     return program_success_code; } /* main */ % gcc -o charstrassnbad charstrassnbad.c charstrassnbad.c: In function    main   : charstrassnbad.c:8: incompatible types   in assignment The version above seems like it should work, but it doesn   t! Character Strings Lesson CS1313 Spring 2024 9
    10. 
            
            
            
  10. Character String Assignment Example #2 % cat charstrassn.c #include <stdio.h> #include <string.h> int main () { /* main */     const int my_name_length       = 12;     const int program_success_code =  0;     char my_name[my_name_length + 1]; strcpy(my_name, "Henry Neeman"); /* <-- WORKS! */     printf("My name is %s.\n", my_name);     return program_success_code; } /* main */ % gcc -o charstrassn charstrassn.c % charstrassn My name is Henry Neeman. This version works! Character Strings Lesson CS1313 Spring 2024 10
    11. 
            
            
            
  11. #include <string.h> When using string functions in C such as strcpy,                      you MUST add the following preprocessor directive to               your C source file, just after the directive for stdio.h, like so: #include <stdio.h> #include <string.h> Character Strings Lesson CS1313 Spring 2024 11
    12. 
            
            
            
  12. Character String Declaration In C, we declare a character string like so: char my_name[my_name_length+1]; Notice that a character string is declared                             exactly like a char array; in fact, it is a char array. The only difference in the declaration is that the length of       the array of char elements that represents the string is           one greater than the length of the string. Character Strings Lesson CS1313 Spring 2024 12
    13. 
            
            
            
  13. Character String Terminator The last character in any C character string is the                   null character, called NUL, which corresponds to         integer value 0: '\0' Thus, the null character (integer 0) is often referred to as the  character string terminator. In general, a numeric value that is used to indicate that a  particular state has been reached     for example, the end of a  list     is called a sentinelvalue. So, the character string terminator NUL is a sentinel that  indicates the end of the string in question. Character Strings Lesson CS1313 Spring 2024 13
    14. 
            
            
            
  14. How String Printing Really Works #1 % cat charstrassn.c #include <stdio.h> #include <string.h> int main () { /* main */     const int my_name_length       = 12;     const int program_success_code =  0;     char my_name[my_name_length + 1];     strcpy(my_name, "Henry Neeman");     printf("My name is %s.\n", my_name);     return program_success_code; } /* main */ % gcc -o charstrassn charstrassn.c % charstrassn My name is Henry Neeman. The program on the next page behaves identically to this  program. Character Strings Lesson CS1313 Spring 2024 14
    15. 
            
            
            
  15. How String Printing Really Works #2 % cat printstring.c #include <stdio.h> #include <string.h> int main () { /* main */     const int my_name_length       = 12;     const int program_success_code =  0;     char my_name[my_name_length + 1];     int  index;     strcpy(my_name, "Henry Neeman");     printf("My name is ");     index = 0;     while (my_name[index] != '\0') {         printf("%c", my_name[index]);         index++;     } /* while (my_name[index] != '\0') */     printf(".\n");     return program_success_code; } /* main */ % gcc -o printstring printstring.c % printstring My name is Henry Neeman. Character Strings Lesson CS1313 Spring 2024 15
    16. 
            
            
            
  16. String Copy Function: strcpy The C standard library function strcpy copies a character string  into a char array. strcpy(my_name, "Henry Neeman"); Notice that you                                                                      CANNOT SIMPLY ASSIGN ONE STRING TO ANOTHER:  /* THIS WON'T WORK! */   my_name = "Henry Neeman"; /* NO! */ Character Strings Lesson CS1313 Spring 2024 16
    17. 
            
            
            
  17. strcpy Example % cat charstrcpy.c #include <stdio.h> #include <string.h> int main () { /* main */     const int my_name_length       = 12;     const int program_success_code =  0;     char my_name[my_name_length + 1];     char my_name2[my_name_length + 1];     strcpy(my_name, "Henry Neeman");     printf("My name is %s.\n", my_name);     strcpy(my_name2, my_name);     printf("My name is %s.\n", my_name2);     return program_success_code; } /* main */ % gcc -o charstrcpy charstrcpy.c % charstrcpy My name is Henry Neeman. My name is Henry Neeman. Character Strings Lesson CS1313 Spring 2024 17
    18. 
            
            
            
  18. String Placeholder In a printf statement, the placeholder for a character  string is: %s Character Strings Lesson CS1313 Spring 2024 18
    19. 
            
            
            
  19. String Placeholder Example % cat charstrcpy.c #include <stdio.h> #include <string.h> int main () { /* main */     const int my_name_length       = 12;     const int program_success_code =  0;     char my_name[my_name_length + 1];     char my_name2[my_name_length + 1];     strcpy(my_name, "Henry Neeman");     printf("My name is %s.\n", my_name);     strcpy(my_name2, my_name);     printf("My name is %s.\n", my_name2);     return program_success_code; } /* main */ % gcc -o charstrcpy charstrcpy.c % charstrcpy My name is Henry Neeman. My name is Henry Neeman. Character Strings Lesson CS1313 Spring 2024 19
    20. 
            
            
            
  20. The strlen Function The C Standard Library function strlen returns the length  of the string that is passed to it, EXCLUDING THE  STRING TERMINATOR: my_name_length = strlen(my_name); Character Strings Lesson CS1313 Spring 2024 20
    21. 
            
            
            
  21. strlen Function Example % cat charstrlen.c #include <stdio.h> #include <string.h> int main () { /* main */     printf("strlen(%cHenry Neeman%c) = %d\n",         '\042', '\042', strlen("Henry Neeman"));     return 0; } /* main */ % gcc -o charstrlen charstrlen.c % charstrlen strlen("Henry Neeman") = 12 Character Strings Lesson CS1313 Spring 2024 21
    22. 
            
            
            
  22. Dynamic Allocation of Strings You can dynamically allocate the space for a string, just as  you can for any other array: my_name =     (char*)malloc(sizeof(char) *                   (my_name_length + 1)); Character Strings Lesson CS1313 Spring 2024 22
    23. 
            
            
            
  23. String Dynamic Allocation Example #1 % cat charstrdyn.c #include <stdio.h> #include <stdlib.h> #include <string.h> int main () { /* main */     const int program_success_code =  0;     const int program_failure_code = -1;     char* my_name = (char*)NULL;     int   my_name_length; Character Strings Lesson CS1313 Spring 2024 23
    24. 
            
            
            
  24. String Dynamic Allocation Example #2     my_name_length = strlen("Henry Neeman");     my_name =         (char*)malloc(sizeof(char) *                       (my_name_length + 1));     if (my_name == (char*)NULL) {         printf("ERROR: can   t allocate ");         printf("char array my_name.\n");         exit(program_failure_code);     } /* if (my_name == (char*)NULL) */     strcpy(my_name, "Henry Neeman");     printf("My name is %s.\n", my_name);     free(my_name);     my_name = (char*)NULL;     return program_success_code; } /* main */ % gcc -o charstrdyn charstrdyn.c % charstrdyn My name is Henry Neeman. Character Strings Lesson CS1313 Spring 2024 24
    25. 
            
            
            
  25. Passing a String as a Function Argument Passing a string to a function as an argument is                             just like passing  any other kind of array argument,                  whether statically allocated or dynamically allocated,          except that you  DON   T also need to pass a length argument  (because its length is implied by its string terminator): int main () { /* main */     char my_name[my_name_length + 1];     char* my_name2 = (char*)NULL;     ...     print_a_string(my_name);     ...     print_a_string(my_name2);          ... } /* main */ void print_a_string (char* the_string) Character Strings Lesson CS1313 Spring 2024 25
    26. 
            
            
            
  26. String Function Argument Example #1 #include <stdio.h> #include <stdlib.h> #include <string.h> int main () { /* main */     const int my_name_length       = 12;     const int program_success_code =  0;     const int program_failure_code = -1;     char my_name[my_name_length + 1];     char* my_name2 = (char*)NULL;     void print_a_string(char* the_string); Character Strings Lesson CS1313 Spring 2024 26
    27. 
            
            
            
  27. String Function Argument Example #2 strcpy(my_name, "Henry Neeman");     printf("My name is %s.\n", my_name);     print_a_string(my_name);     my_name2 =         (char*)malloc(sizeof(char) *                       (strlen(my_name) + 1));     if (my_name2 == (char*)NULL) {         printf("ERROR: can   t allocate ");         printf("char array my_name2.\n");         exit(program_failure_code);     } /* if (my_name2 == (char*)NULL) */     strcpy(my_name2, my_name);     printf("My name is still %s.\n", my_name);     print_a_string(my_name2);     free(my_name2);     my_name2 = (char*)NULL;     return program_success_code; } /* main */ Character Strings Lesson CS1313 Spring 2024 27
    28. 
            
            
            
  28. String Function Argument Example #3 void print_a_string (char* the_string) { /* print_a_string */     const int program_failure_code = -1;     printf("The string that was passed is:\n");     if (the_string == (char*)NULL) {         printf("ERROR: can   t print a ");         printf("non-existent string\n");         printf(" in print_a_string.\n");         exit(program_failure_code);     } /* if (the_string == (char*)NULL) */     printf("%s\n", the_string); } /* print_a_string */ % gcc -o charstrpass charstrpass.c % charstrpass My name is Henry Neeman. The string that was passed is: Henry Neeman My name is still Henry Neeman. The string that was passed is: Henry Neeman Character Strings Lesson CS1313 Spring 2024 28
    29. 
            
            
            
  29. String Comparisons Just as numeric values can be compared, so can string values. However, strings aren   t scalars. In C, two strings are defined to be equal if they have             the exact same contents. In C, strings are compared using the strcmp function from  the C Standard Library. The relational operators CANNOT CANNOT CANNOT  be used to compare strings! ==  !=  <  <=  >  >= Character Strings Lesson CS1313 Spring 2024 29
    30. 
            
            
            
  30. String Comparison is Case Sensitive String comparison is case sensitive. Thus, if two strings are identical, except that, in a single  character, they differ by case     for example, an "H" for  one string corresponds to an "h" for the other     then they WON   T be equal. For example: "Henry" is not equal to "henry" Character Strings Lesson CS1313 Spring 2024 30
    31. 
            
            
            
  31. String Comparison Example #1 #include <stdio.h> #include <string.h> int main () { /* main */     const int my_name_length       = 12;     const int program_success_code =  0;     char my_name[my_name_length + 1];     char my_name2[my_name_length + 1];     char my_first_name[my_name_length + 1];     char my_first_name_lower[my_name_length + 1];     char my_last_name[my_name_length + 1]; Character Strings Lesson CS1313 Spring 2024 31
    32. 
            
            
            
  32. String Comparison Example #2 strcpy(my_name, "Henry Neeman");     strcpy(my_name2, my_name);     strcpy(my_first_name, "Henry");     strcpy(my_first_name_lower, "henry");     strcpy(my_last_name, "Neeman");     printf("strcmp(%s,%s) = %2d\n",         my_name, my_name2,         strcmp(my_name, my_name2));     printf("strcmp(%s,%s) = %2d\n",         my_first_name, my_first_name_lower,         strcmp(my_first_name, my_first_name_lower));     printf("strcmp(%s,%s) = %2d\n",         my_last_name, my_first_name,         strcmp(my_last_name, my_first_name));     return program_success_code; } /* main */ Character Strings Lesson CS1313 Spring 2024 32
    33. 
            
            
            
  33. String Comparison Example #3 % gcc -o charstrcmp charstrcmp.c % charstrcmp strcmp(Henry Neeman,Henry Neeman) = 0 strcmp(Henry,henry) = -1 strcmp(Neeman,Henry) = 1 Notice that the return value for strcmp can be interpreted as:     zero:        the strings are equal     negative: the first string is less     positive:  the first string is greater Character Strings Lesson CS1313 Spring 2024 33
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